This week, the Supreme Court begins hearing arguments in two cases that could determine the future of gay marriage in this country. In a few moments, NPR's Nina Totenberg brings us the story of a prominent Republican from the George W. Bush administration who's now working against many in his own party to legalize gay marriage.

But first, another point of view from one of the country's leading evangelical Christian leaders.

JIM DALY: You know, when we look at same-sex marriage or gay relationships, it's just one of the many things that are outside of God's design for human sexuality.

MARTIN: Jim Daly is the president of Focus on the Family, one of several groups sponsoring a march in Washington, D.C. this week, to support what they call traditional marriage: one man, one woman. Mr. Daly says gays and lesbians are as equal as anyone else before God. But he also says gay marriage is a sin, like any other.

DALY: Much like heterosexual men having affairs and those other things. I think for the gay Christian - the person that has a desire in a same-sex, attracted way - I think for that person it's a matter of stewardship and how do they, in their relationship with God, steward their sexuality in a way that honors him and honors the Scripture? That is highly debatable, I understand that. It's even probably inflammatory to some. I'm not the author of the Scriptures. Obviously...

(LAUGHTER)

DALY: ...I'm just trying to read them as carefully as I can and try to live by them, even though I fail. And I think that's one of the big issues is, you know, we're all - according to Scripture - we're all sinners saved by grace. And so, as we look at our human sexuality, which is a very powerful element of the human experience, what God is expecting of us is to bridle that appetite. And for those were married in a traditional male-female context, we give each other for a lifetime to each other. That sounds old-fashioned today in this culture but that is what the Scripture is talking about.

MARTIN: But does it make sense to you that someone could be gay and Christian at the same time?

DALY: Yeah, sure. I mean, in the same way that you can be Christian and commit adultery. Or do something, again, outside of God's stewardship for sexuality. We think it's pretty clear that God's design for human sexuality is a male and a female committed to each other in marriage for life.

And, you know, it's interesting. 'Cause Jesus talks about that in Matthew and Mark in the Gospels, where he restates the Genesis commitment which is: A man shall leave his mother and father and cleave to his wife and the two shall become one. He doesn't say, you know, anything about same-gendered people getting together. And, you know, that's the way we read it.

There is no animus toward the individual, and that's one of the - I think one of the great tragedies of our times, is we've set this up as some super sin or super debate about homosexuality.

MARTIN: Several states legalized gay marriage last fall. Present Obama has come out in support of it. We recently saw leading Republican Rob Portman change his mind on gay marriage, after his son came out as gay.

Are you concerned that the cultural momentum is not moving in your direction? And what does that mean for your message?

DALY: Well, yeah. Again, I'm not overly concerned because I'm not going to stake my sensibility, my spiritual sensibility, in the culture. The culture has changed over the years and this is not new. Greek and Roman empires of millennias(ph) ago, you know, they faced these kinds sexual expressions. And we tend to think that everything is new; isn't this a great, new idea? But humanity has looked at this forever. And I think in the end, even if we go in the direction of allowing same-sex marriage, I think culture at some point will go, whoa, what have we done here.

MARTIN: And last time you and I spoke, you said you do indeed have gay friends. You talk about this issue with them, the issue of gay marriage. I wonder if you've reached out recently, what have those conversations been like?

DALY: Yeah. In fact, one of the things my wife will do - we're going tonight to dinner, Food for Thought. And in this group of about 15 people, there are three gay men in this group and three Christians, and a number of libertarians - left and right people. And it'll be a topic of discussion this very night for me and my wife.

The bigger issue, Rachel, that I'm concerned about is the religious liberty issue attached to all of this. And I think that's the greater danger for the culture.

MARTIN: What do you mean?

DALY: And what I mean by that is the - Kyfel Bloom(ph) who is a good person. She's a self-proclaimed advocate of same-sex marriage rights. She taught at Georgetown University. I think she's now heading up EEOC, the equal employment opportunity group. And I had a chance to talk with her about it. I said, Ky, tell me what a perfect world for you would look like.

And she said: Well, if I wanted to get married to my partner and a Christian person was working at the county courthouse, if they refused to do it - even politely and had somebody else come over to do it - she shouldn't work or he shouldn't work in the county courthouse. What about a doctor that wouldn't do in vitro fertilization for a lesbian couple? Well, they should never be licensed by the state because they would be violating my rights.

So I think the underlying issue here for all of us to consider is that this is going to be deeper than just two people who love each other getting married or having civil union. There's a whole host of religious freedom issues underneath this, that in essence we won't tolerate religious expression any longer; certainly not over sexual preference. And that's a big issue and that's not being talked about in the culture.

MARTIN: Jim Daly, he is the president of Focus on the Family. We spoke with him from Colorado Springs, Colorado. Jim, thanks very much for taking the time.

DALY: Thanks, Rachel.

MARTIN: Next week, we talk with a young man named Jamison Manwaring who recently posted a video acknowledging his homosexuality. We explore within what it's like to grow up gay in a Mormon family. Transcript provided by NPR, Copyright NPR.